Optimized communication system for radio-assisted traffic services

ABSTRACT

An optimized communications system for radio-assisted traffic services such as railroad services. In addition to the fixed-position central services and the fixed-position decentralized control centers, one or more decentralized gateway computers are introduced into the traffic network, with the communication between the mobile objects and the fixed-position objects being provided via the gateway computers.

This application claims priority to International Application No.PCT/DE99/02026 which was published in the German language on Jun. 28,1999.

TECHNICAL FIELD OF THE INVENTION

The invention relates to communications system, and in particular, to anoptimized communications system for radio-assisted traffic services suchas railroad services.

BACKGROUND OF THE INVENTION

Point-based or line-based train influence is used for controllingrailroad operations. In point-based train influence, limited amounts ofspecific information items at fixed-position influencing devices istransmitted to vehicles moving past the devices. The information itemsmay be evaluated, and if necessary, processed further at the device. Inline-based train influence, more information can be exchanged forgreater vehicle control and monitoring. Information can be continuouslytransmitted from a section of the track to the vehicles and, ifnecessary, in the opposite direction. Information is normallytransmitted by means of linear conductors laid in the track, to which atleast individual vehicles of the trains passing through that section areinductively coupled. Due to the complexity of installation, theoperation and maintenance of the linear conductors laid in the track isconsiderable. For this reason, the prior art contemplates data which istransmitted between the individual subscribers by radio. A mobile radiosystem can be used for this purpose, as is already used for voice anddata transmission and is described in EP 0 726 689 A2. The data to betransmitted for controlling railroad vehicles is, in contrast to voiceradio data, safety-relevant since it affects the vehicle controldirectly. Care must therefore be taken in a suitable way to ensure thatthe data cannot be corrupted or lost on their way from the data sourceto the data sink. Cryptographic methods are nowadays widely used for thesecurity of such data.

One special feature of railroad operation is that the data to betransmitted to the trains are produced in a decentralized manner byindividual control stations or control points. Data transmitted vialinear conductors to a train is typically linked to a single controlpoint and, on entering a subsequent section region, is automaticallychanged over to the control point responsible for that section. Withradio train influencing, this automatic association, which is dependenton the decentralized features of the rail system, with the respectivelyresponsible control point is no longer provided. In fact, the vehicle orthe control point responsible for the vehicle for this purpose, and onthe basis of the known location of the vehicle on the section, eitherhas to request the control center set up a link to the train which isapproaching its section region, or cause the vehicle to set up thislink. A specific time interval in the order of magnitude of up to 10 sis in each case required for this purpose. In this time, the locomotiveof a train is still linked to the control center of the section regionover which it is travelling and is thus busy with setting up a link tothe control center of the next region. The vehicle needs to have atleast two radios for this purpose.

One very major problem with regard to data transmission in decentralizedsystems, such as railroad systems, is also presented by the centralservices, for example those for disposition and central diagnosis.Special radio channels are either provided for these central services,although this is scarcely feasible owing to the limited resources, orelse these central services communicate with the trains via thecommunications modules of the decentralized controllers. In the lattercase, however, the link between the central services and the trains mustbe continuously readjusted to match the current locations of the trains.That is, the data for the central services have to be continuallyswitched to the communications modules of the adjacent control centers.This results in gaps in the transmission of data, in particular due tosynchronization processes, in the order of magnitude of several seconds.Furthermore, a disadvantage of this constellation is that centralservices which are making a request to a vehicle must first of alldetermine which control center is currently linked to the relevantvehicle.

In a central communications device according to DE 197 21 246, thesedisadvantages are avoided by introducing an additional central gatewaycomputer which allows a continuous link to the trains, which arepermanently assigned to the gateway computer. The change in the link tothe decentralized objects in this case takes place only on the fixedside between the gateway computer and the decentralized object. Theaccessibility of mobile and fixed objects is in this case provided by afixed relationship between the mobile object and the gateway computer.

This solution has the disadvantages of long communications paths betweenmobile and fixed objects due to the introduction of a fixed-positioncentral gateway computer, via which the communication with the mobilesubscriber takes place irrespective of its location. Furthermore, therelationships between the mobile objects and the gateway computersassociated with them have to be set up and maintained in the vehicle andin the fixed-position gateway computer.

In summary, problems with the known prior art are that, in solutionsbased on the decentralized solution approach, central objects have theproblem of determining those decentralized objects which have a link tothe train, in order to connect to this link. Unknown mobile objectscannot be accessed using this method since no information is availableabout their location in the fixed-position objects. When the responsibledecentralized object changes, a new link is set up to the nextdecentralized object. A second mobile radio is required to do this. Allthe links of the central objects must likewise be changed to the newradio link (hopping).

In implementations based on the central solution approach, each trainhas a fixed substitute in a gateway computer on the section side (fixedrelationship between the mobile object and the gateway computer).Consequently, calls and data always have to be passed via afixed-position node, irrespective of where the train is located. Theresultant communications paths are consequently long, resulting in highoperating costs. Furthermore, the substitute relationships to the mobileobjects have to be configured and maintained individually in eachgateway computer and each mobile object, which leads to high engineeringand maintenance costs.

SUMMARY OF THE INVENTION

In one embodiment of the invention, there is an optimized communicationssystem for radio-assisted traffic services for radio transmission ofdata between mobile objects and central services and fixed-positionobjects, which have decentralized control centers, using at least onegateway computer. Communication between the mobile objects and thefixed-position objects is implemented via the gateway computerssuch-that for the mobile objects which communicate with the gatewaycomputers, one substitute object is in each case set up in the gatewaycomputer and in the fixed-position objects. For the fixed-positionobjects which communicate with the gateway computers, substitute objectsare set up directly in the gateway computer or indirectly via at leastone information server, and an when an update process is used, thesubstitute information in the gateway computer and in the fixed-positionobjects is updated directly between the substitute objects in thegateway computer and the fixed-position objects, or indirectly betweenthe gateway computer and the information server. In one aspect of theinvention, if information servers are connected between the gatewaycomputers and the central services as well as decentralized controlcenters, the update information is cascaded, and compressed informationabout accessible mobile objects is produced in the information server.

In another aspect of the invention, the compressed information can becalled by fixed-position objects.

In still another aspect of the invention, the information serversactively communicate with fixed-position objects and filter and/ordistribute update information.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following textwith reference to exemplary embodiments, at least some of which areillustrated in the figures, in which:

FIG. 1 shows a variant of optimized radio communications by means of adecentralized link map.

FIG. 2 shows a variant of optimized radio communications by means of acentral link map.

FIG. 3 shows a variant of optimized radio communications by means of acentral and decentralized link map.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to an optimized communications system forradio-assisted traffic services which, using simple means, allowsreliable data traffic via effective communications paths with only oneradio transmission channel between the mobile objects and thefixed-position objects, and which minimizes the outlay for setting upthe system, updating the system and maintenance of the system.

One particular advantage of the invention is that, in addition to thefixed-position central services and the fixed-position decentralizedcontrol centers, one or more decentralized gateway computers areintroduced into the traffic network, with the communication between themobile objects and the fixed-position objects being provided via thegateway computers, in such a manner that

-   for the mobile objects which communicate with the gateway computers,    one substitute object is in each case set up in the gateway computer    and in the fixed-position objects, and-   for the fixed-position objects which communicate with the gateway    computers, substitute objects are set up directly in the gateway    computer or indirectly via at least one information server, and-   using an update process, the substitute information in the gateway    computer and in the fixed-position objects is updated directly    between the substitute objects in the gateway computer and the    fixed-position objects, or indirectly between the gateway computer    and the information server.

For example, the gateway computers can be arranged in the vicinity ofswitching nodes, in order to save cable runs.

The communication between mobile and fixed-position objects iscontrolled via the gateway computers. The initiative for communicationcan in this case originate from the mobile end, from central services orfrom decentralized control centers, independently.

In addition to the decentralized gateway computers, information serverscan be set up where required in the railroad network which, asfixed-position objects, can likewise communicate with gateway computers,central services and decentralized control centers.

In order to allow all the links between a mobile object and variousfixed-position objects to be handled using only one radio channel, boththe mobile and the fixed-position end select a common gateway computerfor communication, temporarily and independently on one another.

Setting up substitutes for mobile and fixed-position objects in thegateway computer and updating them in the fixed-position objects ensuresthat the objects can access one another at any time via a common gatewaycomputer. Mobile objects can access all the fixed objects which aremapped as substitutes in the gateway computer via one radio channel.Independently of one another, fixed-position objects can use thesubstitute map to select the correct gateway computer which is thesubstitute object for the vehicle, for example the train, and can thususe a common radio channel to the mobile object.

A further major advantage is that fixed-position objects do not need tostart to search for a gateway computer via which the mobile subscribermay possibly be communicating at the time when they have the requirementto communicate with mobile objects (no polling of gateway computersrequired). Since the information about the communication between thegateway computer and the mobile objects is available, the fixed-positionobject can immediately select the correct gateway computer forconnection to the existing radio link to the mobile object.

Furthermore, the fixed-position object can immediately decide whetherthe desired mobile subscriber is currently communicating with anygateway computer at all. If this is not the case, any desired gatewaycomputer can be selected for communication (possibly based on criteriarelating to an optimum communication path length).

A further advantage is that the described communications system can alsobe used to access mobile subscribers which are unknown to thefixed-position objects (dynamic telephone directory).

The update process optimizes the information transmission in that theonly fixed objects which are informed are those which are alsoregistered in the gateway computer and have a substitute object.Furthermore, only change messages are transmitted between the gatewaycomputer and the registered fixed objects, so that the informationinterchange is also optimized in this respect. The updating informationcan, if necessary, be preprocessed and can be transmitted to the objectswithout any link to the time at which they were created, thus providingbetter distribution of network loads.

No data describing any association between gateway computers and objectsneed be stored in the decentralized gateway computers or in the mobileobjects (no engineering definition).

The traffic network may comprise any desired number of decentralizedgateway computers and information servers, and the network can beexpanded as required.

The requirements for functionality of the traffic network are minimaldue to the introduction of the decentralized, optimized process (forexample no location updating is required in the fixed network).

If additional information servers are connected between the gatewaycomputers and railroad services, there is a further advantage inminimizing information transmission by means of cascading. In thissituation, when change reports occur, each traffic service no longerneed be informed of them directly by means of an update protocol, andthe correction is instead stored centrally in the information server andcan be called up when required by the traffic services. The dynamicinformation for gateway computer selection, if necessary organized onthe basis of the selection criteria, can thus be provided centrally,with minimum communication complexity. This avoids redundant informationin the fixed-position objects.

The present communications system allows the operation of mixedstructures. Information servers can provide information functions forspecific traffic services or specific mobile subscribers (for exampletrains in a generic sense) and thus minimize the update communicationcomplexity, for example in the case of occasional communication withmobile subscribers. In parallel with this, a direct update process bymeans of gateway computers can be provided for further fixed-positiontraffic services or on the basis of defined selection criteria, forexample for frequent communication with mobile subscribers. Thestructures and the communication can thus be matched to the trafficconcern requirements.

Based on the example of railroad service, the communications systemdistinguishes between three components:

-   a) mobile objects (for example trains),-   b) fixed-position gateway computers,-   c) fixed-position objects (central railroad services, decentralized    control devices or information servers).

As illustrated in FIG. 1, a substitute object is set up in the gatewaycomputer for mobile objects which communicate with a gateway computer; asubstitute object is likewise set up in the gateway computer forfixed-position objects which communicate with the gateway computer, andinformation about substitutes for mobile objects for this gatewaycomputer set up in each fixed-position object which has a substituteobject in a gateway computer.

An update process between the substitute objects in the gateway computerand the fixed-position objects updates the substitute information in thegateway computer and in the fixed-position objects when changes occur(for example setting up a new substitute object on establishing radiocommunication with another train.) The update process is optimized tothe requirements for delay time, throughput etc.

The update process means that up-to-date information is always availablein the fixed-position objects relating to which gateway computers arecommunicating with which mobile subscribers. Central services anddecentralized control devices can use the available information todecide whether the mobile subscriber is at present registered in one ofthe known gateway computers and, if so, in which gateway computer. Thisdecision can be used to select the correct gateway computer which isalready communicating with that train. If no substitute informationabout the mobile subscriber is available, a specific selection of thegateway computer can be made (for example with the optimum communicationpath as the criterion).

Information servers can be included for cascading the updateinformation, as illustrated in FIG. 2. In this case, the informationrelating to accessible mobile objects and associated gateway computersis stored in an intermediate, fixed-position information server ratherthan in the central services and decentralized control centers. Anupdate process is used between the information server and gatewaycomputer. Compressed information about accessible mobile subscribers fordifferent gateway computers is thus available in the information server.This information can be called up by other fixed-position objects whichwish to access mobile communications subscribers (information function).If desired, the information server can take the initiative forcommunication with fixed-position objects, and can filter and distributeupdate information (change service). Mixed variants with and without theinterposition of information servers are also feasible, as shown in FIG.3. The respective configuration depends on the communicationrequirements for the applications (for example communication frequency,time requirements).

There are no limits to the number of mobile and fixed-positionsubstitute objects per gateway computer. There are likewise no limits tothe number of gateway computers and information servers which can beinstalled in a railroad network. The method for selection of gatewaycomputers is the same for central servers and decentralized controldevices.

Dynamic functions of the communications system are described in thefollowing text.

I. SIGNALING

IA. Setting up Communication from the Mobile End

Communication is set up by the network (on the basis of definedcriteria) selecting a decentralized gateway computer. A substituteobject for the mobile subscriber is set up in the gateway computer.Controlled by the update protocol, update information about thesubstitute object is then distributed to all the registeredfixed-position objects. These objects thus have the information aboutthe accessibility of the mobile object and about the associateddecentralized gateway computer.

IB. Setting up Communication from the Mobile End

When a mobile object ends communication with the first gateway computer,the substitute object in the first gateway computer is deleted. Theupdate process updates the substitute information for all the registeredfixed-position objects.

IC. Setting up Communication from the Fixed-position End

Any fixed-position object can set up a link to a gateway computer. Ifthere is no need for every fixed-position object to communicate withevery gateway computer, there may be limitations in the fixed-positionobject relating to which gateway computers links should be set up to.Furthermore, there may also be limitations on the selection and scope ofthe update information which is intended to be interchanged between agateway computer and the fixed-position object (for example, only updateinformation relating to high-speed trains may be transmitted, on aselective basis, to the fixed-position object).

When a fixed-position object initiates communication with a gatewaycomputer, a substitute object is set up in this gateway computer. Aprofile about the desired update information can also be set up. Thegateway computer then uses the update protocol to transmit theup-to-date map of the mobile substitute objects (if appropriate selectedon the basis of the update profile criteria) to the fixed-positionobject. The fixed-position object thus has the information about themobile objects which can be accessed from that gateway computer. On thebasis of the available signaling information, a fixed-position railroadservice can set up a data link to the mobile object via the gatewaycomputer that is currently being used by that mobile object.

The fixed-position object which sets up a link to a gateway computer mayalso be an information server. In this case, the directory ofsubstitutes for mobile objects for that gateway computer is set up inthe information server.

Central services and decentralized control centers can eithercommunicate directly with a gateway computer or can receive informationrelating to mobile objects in the gateway computers via informationservers. If an information server is used, the communication between theinformation server and the gateway computer is handled in the same wayas that between the railroad service and the gateway computer withoutany information server. The fixed-position railroad services are in thiscase not included in the update process between the information serverand the gateway computer. The process of setting up a link from thefixed-position object to the mobile object is subdivided into two stepswhere the information server is used.

First: Transmission of signaling information between a fixed-positionobject and an information server. The purpose of this communication isto search for a destination (information about the gateway computer tobe selected). Communication between a fixed-position object and aninformation server may either be initiated by the railroad service(information call), or may be on the initiative of the informationserver (change service). Once signaling has taken place, thecommunication between the fixed-position railroad service and theinformation server is ended.

Second: Setting up the data link between the fixed-position railroadservice and a mobile object via the gateway computer which has beendetermined.

ID. Terminating Communication from the Fixed-position End

When a fixed-position object ends communication with a gateway computer,the update process for this fixed-position object is at an end. Thesubstitute for the fixed-position object in the gateway computer isdeleted. Information relating to changes of substitute objects in thegateway computer will in future no longer be transmitted to thatfixed-position object.

II. DATA TRANSMISSION

Three different types of data need to be transmitted:

-   IIA. Data between mobile objects and decentralized control devices-   IIB. Data between mobile objects and central services-   IIC. Signaling information between gateway computers, information    servers and fixed-position objects (by means of update processes).

The application data traffic for IIA and IIB always passes directly viaa gateway computer without the interposition of any information server.The transmission of the various types of data may be subject todifferent requirements. For example, the transmission of data betweenmobile objects and decentralized control devices may be subject tostringent time and availability requirements. Data type IIB (for examplediagnosis), on the other hand, may have less stringent timerequirements, and may have the character of bulk data. Data such as thiscan be selected, compressed and preprocessed in the gateway computer, ifrequired. Transmission is likewise possible as a function of definedlimit-value criteria or when a radio link is in existence for otherapplications and resources are available. The time of origin of the datacan be decoupled from the time of transmission by intelligentpreprocessing and buffering of data which are not time-critical. Thereis thus no need for data channels to be connected through directly, andthis improves the load distribution in the network. The data for theupdate process IIC are not user data, but are auxiliary information fortransmitting change messages between a gateway computer and the linkedfixed-position objects (central services, decentralized control centersor information servers). If an information server is used, the updatedata are transmitted between the information server and the gatewaycomputer. By accessing the up-to-date directories in the informationserver, fixed-position railroad services can determine the gatewaycomputer responsible for a mobile object, and can then communicate withthat mobile object via this gateway computer. Otherwise, the update dataare transmitted directly between the gateway computer and thefixed-position railroad service.

The invention is not limited to the exemplary embodiments describedhere. In fact, further embodiment variants can be produced by combiningand modifying the means and features, without departing from the scopeof the invention.

1. A communications system for radio-assisted traffic services for radiotransmission of data between mobile objects and central services andfixed-position objects, which have decentralized control centers, usingat least one gateway computer, wherein communication between the mobileobjects and the fixed-position objects is implemented via the at leastone gateway computer such that for the mobile objects which communicatewith the at least one gateway computer, one substitute object is set upin the at least one gateway computer and in the fixed-position objects,and for the fixed-position objects which communicate with the at leastone gateway computer, substitute objects are set up directly in the atleast one gateway computer or indirectly via at least one informationserver, using an update process, substitute information in the at leastone gateway computer and in the fixed-position objects is updateddirectly between the substitute objects in the at least one gatewaycomputer and the fixed-position objects, or indirectly between the atleast one gateway computer and the information server, and wherein ifinformation servers are connected between the at least one gatewaycomputer and the central services as well as decentralized controlcenters, the update information is cascaded, and compressed informationabout accessible mobile objects is produced in the information server.2. The communications system as claimed in claim 1, wherein thecompressed information is configured to be called by fixed-positionobjects.
 3. The communications system as claimed in claim 1, wherein theinformation servers actively communicate with fixed-position objects andfilter and/or distribute update information.